1. Field of the Invention
This invention relates to a variable capacity swash plate compressor in which the piston stroke length changes according to the inclination of the swash plate.
2. Description of the Prior Art
FIG. 1 shows the whole arrangement of a conventional variable capacity swash plate compressor.
The conventional variable capacity swash plate compressor includes a plurality of cylinder bores 106 axially formed through a cylinder block 101, a plurality of pistons 107 slidably received in the respective cylinder bores 106, a thrust flange 140 rigidly fitted on a drive shaft 105, for rotation in unison with the drive shaft 105, a swash plate 110 which has a central through hole 109 through which the drive shaft 105 extends and is tiltable with respect to an imaginary plane perpendicular to the drive shaft 105 and at the same time along the drive shaft 105, a linkage 141 connecting between the thrust flange 140 and the swash plate 110, such that the swash plate is tiltably driven for rotation in unison with the thrust flange 140, a plurality of shoes 150 that slide sliding surface 110a of the swash plate 110 with respect to the circumference of the swash plate 110, a retainer 153 mounted on the swash plate 110 in a manner that allows it to rotate with respect to the swash plate 110, for retaining the shoes 150, and a retainer support plate 155 rigidly fitted on the swash plate 110, for slidably supporting the retainer 153.
A plurality of connecting rods 111 each have one end connected to one of the shoes such that the spherical end may pivot against the shoe 150 and the other end connected to the corresponding piston 107.
FIG. 3 shows the linkage 141 and component parts associated therewith.
The linkage 141 is comprised of a bracket 110e formed on a front-side surface 110c of the swash plate 110, a linear guide groove 110f formed in the bracket 110e such that the guide groove 110f is inclined with respect to the thrust flange-side surface 110c, and a rod 143 screwed into a swash plate-side surface 140b of the thrust flange 140. The rod 143 has one spherical end portion 143a that is slidably fitted in the guide groove 110f.
Torque from an engine, not shown, installed on an automotive vehicle, not shown, is transmitted to the drive shaft 105 to rotate the same. Torque from the drive shaft 105 is transmitted from the thrust flange 140 to the swash plate 110 via the linkage 141 to cause rotation of the swash plate 110 about the drive shaft 105. As the swash plate 110 rotates, the shoes 150 slide against the sliding surface 110a of the swash plate 110, along the circumference of the swash plate 110, whereby torque transmitted from the swash plate 110 is converted into the reciprocating motion of the piston 107.
The linkage 141 best shown in FIG. 3 provides the following advantageous effects.
When thermal load on the compressor decreases to produce a moment acting on the swash plate 110 for reducing the inclination angle of the swash plate 110, the center of rotation of the swash plate 110 (i.e. a point of intersection between the axis of the rod 143 and a Y-axis orthogonal to the axis of the drive shaft 105) moves in a direction away from the axis of the drive shaft 105, so that the moment acting on the swash plate 110 is decreased, and when the swash plate 110 tilts through an angle which nulls the moment, control of the compressor becomes stable. The linkage 141 can be assembled with ease, and since the spherical end 143a of the rod 143 is slidably fitted in the guide groove 110f (in point contact with the same), pinching of the spherical end 143a in the guide groove 110f hardly occurs even if it is not assembled with a high degree of accuracy.
What should be noted here is that when the compressor is in operation, the swash plate 110 always receives compression reaction forces (the sum of them is represented by P) from the compressing pistons 107 as well as tensile reaction forces (the sum of them is represented by T) from pistons during the suction stroke 107 (see FIG. 3). More specifically, approximately half of the outer peripheral portion (compressing piston-side area) of the swash plate 10 receives the compression reaction forces P, while the other approximately half of the outer periphery (suction piston-side area) of the same receive the tensile reaction forces T. In FIG. 1, the viewer's side (the same as the front side of the sheet of FIG. 1) of the outer periphery of the swash plate 110 with respect to an imaginary plane including the axis of the drive shaft 105 (X-axis) and an axis (Y-axis) which is orthogonal to the axis of the drive shaft 105 and extends on a plane including a top dead center position point of the swash plate and a bottom dead center position point of the same (which extends along a direction of inclination of the swash plate) is the compressing piston-side area, while a remote side (the same as the reverse side of the sheet of FIG. 1) of the outer periphery of the swash plate 110 with respect to the same imaginary plane is the suction piston-side area. In FIG. 3, the upper half of the outer periphery of the swash plate 10 with respect to the axis (X-axis) of the drive shaft 5 is the suction piston-side area, while the lower half of the outer periphery of the same is the compressing piston-side area.
FIG. 4 shows distribution of the compression reaction forces and tensile reaction forces acting on the swash plate. FIG. 2 is a view taken on line A--A of FIG. 1.
If the sum P of the compression reaction forces (these forces or components of the sum P are represented by F1, F2, and F3) acting on the compressing piston-side area of the swash plate 110 is as large as the tensile reaction forces (these forces or components of the sum T are represented by Fi, . . . ) acting on the suction piston-side area of the swash plate 110, and at the same time acting in the same directions parallel to each other at respective locations equally distant from the rotation axis of the drive shaft 105, the two kinds of forces cancel each other to thereby maintain the swash plate 5 in a balanced state.
However, the compression reaction forces act in an opposite direction to the tensile reaction forces, so that torsion moment MT on a fulcrum of P1 or about the Y-axis (in a clockwise direction as viewed in FIG. 2) is produced.
As a result, edges L and R of the central through hole 109 of the swash plate 110 receive the torsion moment MT.
If the torsion moment MT is large, the swash plate 110 is hindered from sliding smoothly along the drive shaft 105, which results in degradation of controllability of the compressor as well as abrasion of contact portions (edges L and R) of the swash plate 110 against the drive shaft 105. Seizure of the compressor may result therefrom.